One or more aspects of the present invention relate, in general, to processing within a computing environment, and more particularly, to processing an instruction fetch from an instruction cache of the computing environment.
As is well known, a processor is a computing device that executes instructions to operate upon data in a computing environment. The instructions used by the processor are generally stored in memory. Typically, a processor may include one or more cache memories to allow faster access to frequently used instructions, and/or data. These cache memories may include an instruction cache and a data cache.
The instruction cache is typically divided into multiple cache lines, each having multiple cache line segments of instructions, and accesses or fetches to instructions are typically performed in a sequential manner. Consequently, when an instruction cache line includes, for instance, four or eight cache line segments, typically all four or eight cache line segments of the cache line may be accessed in a sequential manner. By way of example, a 32-byte line segment size may equate to 8 instructions, which means that a cache line holding 128 or 256 bytes would equate to 32 or 64 instructions, respectively, in the cache line.
Commonly, an instruction cache may have associated therewith one or more directories, such as an instruction directory (IDIR), which contains for each cache line in the cache the address of the memory location that is stored in that cache line. If the cache is set associative, then the instruction directory is also set associative. Additionally, the one or more directories may include an instruction translation lookaside buffer (ITLB) containing virtual address to physical address mapping. The instruction translation lookaside buffer is sometimes alternatively referred to as an instruction effective-to-real address translation (IERAT) directory.
Typically, for each cache access, one or more cache-related directory accesses are performed to obtain, for instance, the corresponding cache-directory entry to verify its correctness.